The suspected shooter, who barricaded himself in a home in Mount Vernon, was taken into custody after midnight Friday. The suspect was not identified.
Law enforcement officials initially said that the suspect -- described by police as a 44-year-old Mount Vernon man -- had taken hostages, but they later said that was not the case.
Two other men are also in police custody. Officials described them as "persons of interest."
"He is a violent offender and well-known to law enforcement," Washington State Patrol Sgt. Keith Leary had told reporters Thursday night of the suspected shooter.
Multiple law enforcement agencies responded, as did negotiators, KOMO reported.
Police officers in Mount Vernon responded to a domestic disturbance around 5:30 p.m., ABC affiliate KOMO reported, citing Washington State Patrol.
When officers arrived, the suspected shooter barricaded himself inside a home and started to shoot at officers, Washington State Patrol Sgt. Leary said.
An officer was shot in the back of the head, and initially transported conscious and alert to nearby Skagit Valley Hospital, Sgt. Leary said. The officer was then airlifted to Seattle's Harborview Medical Center. A spokeswoman for the hospital had told The Associated Press that the officer was in surgery as of 10:30 p.m. But by early Friday morning, KOMO reported that the officer was out of surgery and in serious but stable condition.
According to The Associated Press, the officer is 61-years-old and has about 30 years of service.
Neighbors were evacuated to a nearby church, Sgt. Leary said.
ABC News' Matt Foster contributed to this report.